In a wireless communication system, a base station provides a plurality of user equipments with services. The base station schedules user data with respect to the plurality of user equipments and transmits control information, including scheduling information, to the user equipments together with the user data. A channel carrying the control information is called a control channel and a channel carrying the user data is called a data channel. The user equipments search the control channel to find its own control information and process its own data using the control information.
Before receiving the user data, the user equipment needs to receive the control information. Because the control information is information on decoding of the user data. However, it is common that in a given bandwidth, some pieces of control information of several user equipments are multiplexed within one transmission interval. That is, the base station multiplexes the control information for a plurality of user equipments and transmits the multiplexed control information.
A scheme in which a user equipment receives its own control information of the multiplexed control information is blind detection. The blind detection is a method in which a user equipment decodes the entire data until its own data is found in a situation where the user equipment does not know whether it own data is transmitted from a base station. That is, the user equipment decodes the entire multiplexed control information until its own control information is found in a situation where the user equipment does not know at which part of the multiplexed control information is its own control information placed. The user equipment can employ its unique information in order to determine whether the control information is its own control information. For example, when multiplexing control information of each user equipment, the base station masks an identifier (ID) of each user equipment to a cyclic redundancy check (CRC) of the control information. Each user equipment can determine its own control information by demasking its own ID to the CRC of the control information.
If the user equipment does not correctly detect its own control information from the multiplexed control information, the user equipment cannot decode subsequent user data. Thus, rapid and correct detection of control information plays an important role in the performance of the system. However, there may be a difficulty in detecting control information through only the blind detection.
Each user equipment may require different control information and employ channel encoding using a different code rate. Thus, the size of control information may be different every user equipment. In this case, since offset for blind detection becomes small, the number of detection attempts can be much increased. Further, control information is information unrelated to user data. If the size of the control information increases, it acts as overhead. As the number of user equipments increases, complexity required to decoding control information may increase.
Accordingly, a method is sought for efficiently receiving control information from multiplexed control information.